Ukrainian soldiers secure a checkpoint in the town of Mariupol, eastern Ukraine on Aug. 27, 2014. / Sergei Grits, AP

by Anna Arutunyan, Special for USA TODAY

by Anna Arutunyan, Special for USA TODAY

MOSCOW - A number of Russian soldiers are being killed or going missing, human rights activists say, amid growing evidence suggesting the casualties are the result of Russian military involvement in neighboring Ukraine.

Sergei Krivenko, of Russia's Presidential Human Rights Council, said a woman reported her son's body was brought to her home last week, with documents saying he died of his wounds, but not where he had died.

"She called other soldiers who served with her son," he said. "They told her he was killed among 100 others" in a rocket attack in Ukraine's Donetsk region, where much of the fighting between pro-Russian separatists and the Ukrainian military has been focused.

Earlier this week, the council filed a report with the Investigative Committee of the Russian Federation over the deaths of nine contract soldiers of a mechanized infantry division in a training area in the Rostov region, which borders Ukraine.

"These aren't just civilians, but people who are following (military) orders," Krivenko said. "That is why we asked that these deaths be investigated."

Sending soldiers to areas of military confrontation and not officially reporting their deaths was a common practice during the Soviet war in Afghanistan, and similar incidents occurred during Russia's first military conflict in separatist Chechnya in 1994.

While deaths during training do occur in peacetime, Krivenko said they are normally investigated and confirmed immediately. That has not been the case this time.

The reports are sparking fears among relatives of soldiers who are being sent to areas near the Ukrainian border.

Krivenko said his agency has been getting letters from parents of conscripts and contract soldiers who are being sent to the Rostov region for training, but parents fear they will be crossing the border into Ukraine.

"I am getting calls from people asking what to do, with (conscripts) being pressed to sign up as contract soldiers (to be sent to the border)," said Lidia Sviridova, head of a regional Soldiers' Mothers committee in Saratov. The group is a Russian non-governmental organization protecting the rights of conscripts.

The concerns come amid new escalation in months-long fighting between Ukrainian authorities and pro-Russian separatists in the country's east. The U.S. and Ukraine say large numbers of Russian tanks have crossed the border this week into Ukraine in a "full-scale" invasion.

Russian forces, she said, are being sent 30 miles inside Ukraine, without them or their families knowing where they are going. Psaki cited reports of burials in Russia for those who've died in Ukraine and wounded Russian soldiers being treated in a St. Petersburg hospital.

There could be as many as 15,000 Russian troops in Ukraine, many of them deployed there without official documents, said Valentina Melnikova, head of the Committee of Soldiers' Mothers.

"The government is disavowing soldiers who are there," she said.

The Russian government, meanwhile, continues to vehemently deny it is supplying weapons and expertise to the rebels. Alexander Zakharchenko, prime minister of the self-proclaimed Donetsk People's Republic, conceded Thursday that up to 4,000 Russians were fighting alongside rebels, but doing so strictly as volunteers, ITAR-Tass reported.

Photographs emerged in the local Russian news media Monday of the burial of two soldiers of the 76th Airborne Division in the northern Russian city of Pskov, but relatives of those killed refused to talk to journalists.

Memorials on the fresh graves said that Leonid Kichatkin and Alexander Osipov died on Aug.19 and Aug. 20, respectively. Around the same dates, the Ukrainian military captured a BMD-2 infantry fighting vehicle that it said belonged to the Pskov Airborne Division.

Photographs of a roll-call journal found at the site and published by Ukrainian journalist Roman Bochkala included Kichatkin's name. However, a Russian Defense Ministry spokesman called the authenticity of the journal into question, saying such documents were no longer in use.

After capturing 10 Russian paratroopers earlier this week, Ukrainian Defense Minister Valery Geletey urged Russians whose sons or husbands were serving in the armed forces to find out if they had been sent to Ukraine.

"Today the Ukrainian Armed Forces have captured a lot of Russian servicemen," he wrote on his Facebook page Monday. "Officially they are undergoing training in various corners of the Russian Federation. But in reality, they are taking part in armed aggression against Ukraine. I am addressing relatives of Russian servicemen. Immediately find out where your loved ones really are. Take them out of Ukraine."

However, Russia's Airborne Troops Union, an association of veterans, said it had no reports or complaints of any soldiers dying or going missing.

"There may be veteran paratroopers crossing the border into Ukraine as volunteers, but this is not legal," said Nikolai Belyayev, acting chairman of the union's council. "We've had a lot of requests from veterans who want to go as volunteers and fight on the side of the (self-proclaimed) Donetsk and Luhansk People's Republics, but this is not allowed by the law, so we do not facilitate it.

"However, I know several people who are fighting as volunteers."

Still, relatives of other soldiers serving in the Russian Armed Forces are finding their names on lists of those killed or captured by Ukrainian forces published by journalists and bloggers. While the authenticity of the lists has been questioned, seeing a loved one's name on it is enough to spark panic.

"The connection (with soldiers) is lost. They are afraid, they fear tragedy," Yuri Tikhomirov, of the Kostroma regional Committee of Soldiers' Mothers, said. "Wives, mothers are coming to us."

Saratov resident Lyubov Maksimova grew worried Aug. 21, when photos of her son Ilya's personal items showed up online, along with his name on a list of those who had died in Ukraine. Ilya, a serviceman in the airborne troops, had stopped calling her a few days prior. "He used to call every day before that," she said.

After going public with her concerns, Maksimova's family got a call from an unknown number, with an unidentified man telling them they would be speaking to their son.

Ilya spoke briefly, only to say that he was alive and well on a training ground in Rostov across the border from Ukraine, Maksimova said. "I don't know anything else," she added.